1. Field of Invention
This invention relates to an alloy plating bath for providing electroplated deposits of chromium alloy, such as, for example, Cr--Fe, Cr--Fe--Ni, Cr--Ni.
2.Discussion of Prior Art
Many different compositions have been attempted for use in Cr-alloy plating baths, such as, for example, sulfate bath, sulfamic acid bath, chloride bath, chromic acid bath, and fluoborate bath. However, these bath compositions were not practical for industrial use, for a variety of reasons. For example, the chromic acid bath or the fluoborate bath produce deposits of undesirable properties. Also, the solutions of these baths are harmful in handling, and hence, are excluded from practical applications.
Furthermore, the sulfate bath, the sulfamic acid bath and the chloride bath always contain a pH buffer, such as boric acid, a complexing agent, such as citric acid or EDTA, or other organic additives. Thus, although they could produce satisfactory deposits during initial periods of the plating proces, the baths become unstable during electrolysis. In addition, as a substantial problem, uniformity of deposits is deteriorated due to generation of trivalent Fe ion or hexavalent Cr ion, by anodic oxidation. In order to prevent such deterioration a diaphragm is usually provided between the anolyte and the catholyte. However, this is not a practical solution to the problem. For these reasons, it was difficult to use conventional baths for industrial applications.